At boundaries of oxygen minimum zones (OMZs), bathyal faunas experience steep gradients in oxygen and organic-matter availability. The present study compares changes in microbial, meiofaunal, macrofaunal and megafaunal benthic assemblages along these gradients on Volcano 7, a 2.3-km high seamount in the eastern tropical Pacific. Faunal tolerance to dysaerobic (low oxygen) conditions varies with organism size; microbial and meiofaunal abundances are less affected than macro- and megafaunal abundances. At the exceedingly low concentrations (< 0.1 ml/1) encountered on the upper summit of Volcano 7, oxygen appears to exert primary control over abundance, composition and diversity of macrofauna, overriding other factors such as food availability and sediment grain size. When oxygen concentration is sufficient, food availability in sediments (indicated by the presence of labile material such as chlorophyll a) is highly correlated with meiofaunal and macrofaunal abundance. Four distinct physical zones were identified on Volcano 7: (1) the coarse-grained upper summit zone (730-770 m) where near-bottom oxygen concentrations were usually lowest (often < 0.1 ml/1) and organic-matter (% organic carbon and chlorophyll a) availability was high, (2) the coarse-grained lower summit (770-1000 m) where near-bottom oxygen concentrations were usually slightly higher (0.11 to 0.16 ml/1) and organic-matter availability remained high, (3) the coarse-grained flank (1000-2000 m) where oxygen concentration was intermediate (0.7-0.9 ml/1) and sediment organic-matter content was very low, and (4) the finer-grained base (2000-3500 m) where oxygen values exceeded 2.5 ml/1, sediment organic carbon was moderate, and chlorophyll a was low. Abundances of larger forms (megafauna and macrofauna) were severely reduced on the upper summit, but attained high values (2.25/m2 and 8,457/m2 respectively) just tens of meters below. The smaller forms (bacteria and meiofauna) attained peak abundances on the low-oxygen upper summit, however, abundances of harpacticoid copepods were greatly reduced on the upper and lower summit, presumably due to oxygen limitation. Macrofaunal abundance and diversity patterns along the Volcano 7 oxygen/enrichment gradient resembled those typically observed along shallow-water gradients of organic pollution. Low densities of a few soft-bodied, low-oxygen tolerant species resided on the upper summit, a high-density, low-diversity assemblage inhabited the lower summit, and low-density, high-diversity assemblages occupied the flank and base sediments. The infaunal communities on Volcano 7 support the idea that OMZ boundaries are regions of enhanced biological activity. Modern faunal distributions and biogenic structures at OMZ boundaries may be useful in reconstructing oxygenation histories of ancient marine basins.

The objective of this study was to determine if biogenic features such as mounds, pits and tubes produce small-scale (0.1-100 m) spatial heterogeneity in macrofaunal community structure on the continental slope off North Carolina at 850 m. Macrofaunal and microbial communities associated with sediment mounds, pits and level areas were compared off Cape Lookout, North Carolina. No significant differences were found in sediment microbial counts or total macrofaunal distributions. One paraonid polychaete (Levensenia gracilis) was more abundant in pits than in the other samples, and infaunal anemones exhibited depressed densities in sediment mounds. At a second site, off Cape Hatteras, North Carolina, infaunal heterogeneity associated with the tube-building foraminiferan Bathysiphon filiformis was examined by comparing an area with high tube densities (93.8 m(-2)) with an area 100 m away without tubes. No significant differences were found in the distribution and abundances of bacteria between the two areas. The only significant difference found in infaunal densities was the presence of high numbers of reproductive oligochaetes in the 5-10 cm fraction beneath tube beds. One terebellid polychaete species (Nicolea sp.), which lives exclusively on B. filiformis tubes, was absent in the non-tube area. With a few exceptions, the biogenic structures examined at these two sites appeared to exert only minor influence on macrofaunal or microbial community structure. Within each site, slope assemblages examined in this study appeared to be homogeneous on the small scales examined.

The influence of seamount-intensified flows on the structure of infaunal assemblages was examined at two sand-covered sites located 2.3 km apart atop the summit plain of Fieberling Guyot (32-degrees 27.6'N 127-degrees 48.0'W). Both sites experience strong, tidal bottom currents with flows exceeding 20 cm/ s on a daily basis (4 mab). Estimates of shear velocity (u*) did not differ significantly between the two sites. However, differences in sediment composition and density produced different sediment transport regimes at the two sites. At Sea Pen Rim (SPR), located on the NW perimeter (635 m), sedimentary particles were composed primarily of basaltic sands that experienced negligible transport during the study period. At White Sand Swale (WSS, 580 m), a narrow valley enclosed on three sides by basalt outcrops, sediments were composed almost entirely of foraminiferal sands that moved daily. Sediment organic content and microbial abundances were similar at the two sites. Infauna (> 300 mum) had higher densities at WSS (1870/m2) than SPR (1489/m2), but lower expected species richness. Although the 2 sites shared nearly 50% of identified species, peracarid crustaceans, echinoderms, sponges, and bryozoans were proportionally more important in the stable substrates of SPR, while turbellarians, bivalves, and aplacophorans were better represented in the shifting sands of WSS. The infauna of WSS lived deeper in the sediment column (> 50% below 2 cm) than that of SPR (> 50% in the upper 1 cm), at least partly because the majority (83%) at WSS were subsurface burrowers with motile lifestyles. Tube-building and epifaunal lifestyles were more common at SPR than WSS, as were surface-deposit and filter-feeding modes. Fences and weirs were deployed at the study sites for 6.5-wk and 6-mo periods to manipulate bottom stress. Changes in faunal patterns within weirs at WSS reinforced our conjecture that contrasting sediment transport regimes explain between-site differences in community structure. Fence effects varied with deployment period and site. Topographic features on Fieberling Guyot produce heterogeneous sedimentary settings characterized by different transport regimes. Our results suggest that substrate mobility exerts primary control over infaunal community structure at the two high-energy sites.

Rates and mechanisms of infaunal recolonization in contrasting sediment transport regimes were examined by deploying hydrodynamically unbiased colonization trays at 2 sites similar to 2 km apart on the flat summit plain of Fieberling Guyot in the eastern Pacific Ocean. Both study sites experienced strong bottom currents and high shear velocity (u* exceeding 1.0 cm s(-1) daily). Macrofaunal recolonization of defaunated sediments on Fieberling Guyot was slow relative to observations in shallow-water sediments, but rapid compared to other unenriched deep-sea treatments. Microbial colonization was slower but macrofaunal colonization was faster at White Sand Swale (WSS, 585 m), where rippled foraminiferal sands migrate daily, than at Sea Pen Rim (SPR, 635 m), where the basaltic sands move infrequently. Total densities of macrofaunal colonizers at WSS were 31 and 75% of ambient after 7 wk and 6.4 mo, respectively; at SPR they were 6 and 49% of ambient, respectively. Over 3/4 of the colonists were polychaetes (predominantly hesionids and dorvilleids) and aplacophoran molluscs. Species richness of colonizers was comparable at SPR and WSS and did not differ substantially from ambient. Most of the species (91%) and individuals (95%) recovered in colonization trays were taxa present in background cores. However, only 25% of the taxa colonizing tray sediments occurred in trays at both WSS and SPR. Sessile species, carnivores and surface feeders were initially slow to appear in colonization trays, but after 6.4 mo, colonizer feeding modes, life habits and mobility patterns mirrored those in ambient sediments at WSS and SPR. Defaunated sediments were colonized by larvae, juveniles and adults at both sites. These experiments provide the first observations of infaunal colonization on seamounts, and in deep, high-energy settings. Passive bedload transport appears to be a dominant colonization mechanism in unstable foraminiferal sands at WSS. Based on the rapid recovery of infauna in trays and low diversity at WSS, we infer that disturbance is a natural feature of this site and that the ambient fauna of WSS retains features of early succession. Infaunal colonization is slower in the stable substrate at SPR, where physical disturbance may occur much less frequently.

Early succession of macrofauna was examined over several years in a created Spartina alterniflora marsh located on the Newport River Estuary, North Carolina, USA. Epifauna and infaunal community structure and composition were compared at 2 elevations in plots planted with S. alterniflora, plots left bare of vegetation and vegetated plots in a nearby natural S, alterniflora marsh. No significant successional differences were observed between vegetated and unvegetated sediments in the created marsh. The earliest stages of colonization involved recruitment by opportunistic estuarine polychaetes: Streblospio benedicti, Capitella spp, and Polydora cornuta. Capitella spp. dominated the macrofauna a month after marsh creation, but thereafter S. benedicti was the most abundant species. During the first few years, the artificial marsh retained early successional characteristics, with S, benedicti, Capitella spp. and turbellarians accounting for 75 to 95% of the total macrofauna. Fiddler crabs were common epifaunal colonists. After 4 yr, species richness increased and dominance by the early colonists diminished. Taxa lacking planktonic larvae and swimming adults were particularly slow to recover in the created marsh, but accounted for over 25% of the infauna by Year 4. Oligochaetes, which comprised over 50% of the fauna in the natural marsh, remained absent or rare in the artificial system throughout the study. Infaunal recovery appears to be more rapid in lower than upper marsh elevations. Although macrofaunal densities and species richness of sediments in the lower created marsh came to resemble those of the natural marsh within 6 mo, species composition and faunal feeding modes did not. These observations suggest there may be significant functional differences between young artificial marshes and older natural marshes. Consideration of the timing of marsh creation, marsh configuration, continuity with natural marshes, seeding of taxa with poor dispersal, and attention to species habitat requirements are recommended to accelerate infaunal colonization of created Spartina marshes.

Mudball-building cirratulid polychaetes have been described previously only from the southern California margin. During a study of oxygen minimum-zone benthos in fall 1994, we observed dense aggregations of agglutinated mudballs at 840 to 875 m on the Oman margin in the northwest Arabian Sea. These were inhabited, and probably constructed, by a cirratulid polychaete species in the genus Monticellina. The mudballs were cigar-shaped, 4.5 to 25 mm long, and positioned vertically so as to protrude several millimeters above the sediment-water interface. Total mudball densities were similar to 16000 m(-2). Occupied mudballs occurred at densities of 2112 m(-2); 89% were in the uppermost 2 cm of sediment, and no occupied mudballs were found below 10 cm. Organisms other than the cirratulid were present on 1.7% of the mudballs examined, and included epizoic polychaetes, agglutinated and calcareous Foraminifera. Various polychaetes, a nemertean and nematodes were found inside tests. Mudball abundance exhibited positive associations with densities of several paraonid polychaete species, and with densities of burrowing and subsurface-deposit-feeding polychaetes. Negative associations were observed between mudballs and three tube-building taxa (two polychaetes and an amphipod). Mudball-inhabiting cirratulids are abundant in at least two low-oxygen, margin settings. We expect further sampling of bathyal environments to yield additional systems in which cirratulid mudballs are common. Such observations are valuable because mudballs appear to represent a significant source of heterogeneity that can influence macrofaunal community structure in deep-sea sediments.

The relationships of environmental factors with measures of macrobenthic community diversity were examined for the total fauna, and for polychaetes only, from 40 bathyal stations in the North Atlantic, eastern Pacific and Indian Oceans (154-3400 m). Stepwise multiple regression revealed that depth, latitude, sediment organic-carbon content and bottom-water oxygen concentration are significant factors that together explained 52-87% of the variation in macrobenthic species richness (E[s(100)]), the Shannon-Wiener index (H'), dominance (D), and evenness (J'). Percent sand and percent clay were not significant factors. After removal of depth and latitudinal effects, oxygen and organic-carbon concentrations combined accounted for 47, 67, 52 and 32% of residual variation in macrobenthic E(s(100)), H', D, and J', respectively. Organic carbon exhibited a stronger relationship than oxygen to measures of community evenness, and appeared to have more explanatory power for polychaetes than total macrobenthos. When only stations with oxygen < 1mll(-1) were considered, oxygen concentration became the dominant parameter after depth. Results suggest existence of an oxygen threshold ( < 0.45 mi l(-1)), above which oxygen effects on macrobenthic diversity are minor relative to organic matter influence, but below which oxygen becomes a critical factor. Our regression results lead us to hypothesize that for bathyal faunas, oxygen at low concentrations has more influence on species richness, while organic carbon regulates the distribution of individuals among species (community evenness). Examination of rarefaction curves for Indo-Pacific stations reveals that total macrobenthos, polychaetes, crustaceans and molluscs all exhibit reduced species richness within oxygen minimum zones (OMZs). However, representation under conditions of hypoxia varies among taxa, with polychaetes being most tolerant. Molluscs and crustaceans often (but not always) exhibit few individuals and species in OMZs, and sometimes disappear altogether, contributing to reduced macrobenthic diversity and elevated dominance in these settings. The linear negative relationship observed between bathyal species richness and sediment organic-carbon content (used here as a proxy for food availability) may represent the right side (more productive half) of the hump-shaped, diversity-productivity curve reported in other systems. These analyses suggest then are potentially strong influences of organic matter and oxygen on the diversity and composition of bathyal macrobenthos, especially in the Indo-Pacific Ocean. (C) 1998 Elsevier Science Ltd. All rights reserved.

It has been argued that strong near-bottom hows affect macrofauna and meiofauna in the deep sea, but the evidence comes largely from studies that compared sites separated geographically by hundreds to thousands of kilometers and in depth by hundreds of meters. In this paper, the results of the first experimental investigation of the effects of strong near-bottom flow on deep-sea metazoan meiofauna are presented. At a site (32 degrees 27.581' N, 127 degrees 47.839' W) at 583 m depth on the Fieberling Guyot summit plain, the submersible Alvin emplaced weirs designed to increase the near-bottom flow locally. After 6.5 weeks, sediments in the weirs and unmanipulated locations in the vicinity were sampled. The abundances of nematodes, harpacticoid copepods, ostracods, and kinorhynchs, considered collectively and as individual taxa, were significantly lower in the weir samples than in the background samples. Parallel responses were observed in total macrofaunal and mollusk abundances. Proportional declines in kinorhynchs and mollusks were observed as well. These results suggest that strong near-bottom flow can reduce the abundance of meiofauna and macrofauna in the deep sea and alter assemblage composition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32 degrees 27.631'N, 127 degrees 49.489'W; 32 degrees 27.581'N, 127 degrees 47.839'W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects. (C) 1999 Elsevier Science Ltd. AII rights reserved.

Ecosystem recovery following wetland restoration offers exceptional opportunities to study system structure, function, and successional processes in salt marshes. This study used observations of natural variation and large-scale manipulative experiments to test the influence of vascular vegetation and soil organic matter on the rate and trajectory of macrofaunal recovery in a southern California created salt marsh, the Crown Point Mitigation Site. During the first three years following marsh establishment, macrofaunal density and species richness recovered rapidly within the Spartina foliosa (cordgrass) zone; densities in the created marsh were 50% of those in the natural marsh after 16 mo and 97% after 28 mo. However, the early successional assemblage had a lower proportion of tubificid and enchytraeid oligochaetes, and a higher proportion of chironomids and other insect larvae than did the mature natural marsh. Most of the colonizers arrived by rafting on sea grass and algae rather than by larval dispersal. Initial planting of S. foliosa had no influence on macrofaunal recovery, perhaps because of variable transplant survival. However, subsequently, both positive and negative correlations were observed between densities of some macrofaunal taxa and shoot densities of S. foliosa or Salicornia spp. (pickleweed). Salinity and measures of soil organics (belowground biomass, combustible organic matter, and chlorophyll a) also were correlated with macrofaunal densities and taxon richness. Of foul added soil amendments (kelp, alfalfa, peat, and Milorganite), Milorganite (a sewage product) and kelp both promoted macrofaunal colonization during year 1, but effects were short lived. The most significant sources of heterogeneity in the recovering marsh were associated with site history and climate variation. Faunal recovery was most rapid in highly localized, organic-rich marsh sediments that were remnants of the historical wetland. Elevated sea level during the 1998 El Nino corresponded with similarity of macrofaunal communities in the created and natural marshes. The large spatial scale and multi-year duration of this study revealed that natural sources of spatial and temporal heterogeneity may exert stronger influence on faunal succession in California wetlands than manipulation of vegetation or soil properties.

In coastal wetlands, invasive plants often act as ecosystem engineers altering flow, light and sediments which, in turn, can affect benthic animal communities. However, the degree of influence of the engineer will vary significantly as it grows, matures and senesces, and surprisingly little is known about how the influence of an ecosystem engineer varies with ontogeny. We address this issue on the tidal flats of San Francisco Bay where hybrid Spartina (foliosa x alterniflora) invaded 30 years ago. The invasion has altered the physico-chemical properties of the sediment habitat, which we predicted should cause changes in macrofaunal community structure and function. Through mensurative and manipulative approaches we investigated the influence of different growth stages of hybrid Spartina on macrobenthos and the underlying mechanisms. Cross-elevation sampling transects were established covering 5 zones (or stages) of the invasion, running from the tidal flat (pre-invasion) to an unvegetated dieback zone. Additionally, we experimentally removed aboveground plant structure in the mature (inner) marsh to mimic the 'unvegetated areas'. Our results revealed four distinct faunal assemblages, which reflected Spartina-induced changes in the corresponding habitat properties along an elevation gradient: a pre-invaded tidal flat, a leading edge of immature invasion, a center of mature invasion, and a senescing dieback area. These stages of hybrid Spartina invasion were accompanied by a substantial reduction in macrofaunal species richness and an increase in dominance, as well as a strong shift in feeding modes, from surface microalgal feeders to subsurface detritus/Spartina feeders (mainly tubificid oligochaetes and capitellid polychaetes). Knowledge of the varying influence of plant invaders on the sediment ecosystem during different phases of invasion is critical for management of coastal wetlands.

Geological, biological and biogeochemical characterization of the previously unexplored margin off Unimak Island, Alaska between 1965 and 4822 m water depth was conducted to examine: (1) the geological processes that shaped the margin, (2) the linkages between depth, geomorphology and environmental disturbance in structuring benthic communities of varying size classes and (3) the existence, composition and nutritional sources of methane seep biota on this margin. The study area was mapped and sampled using multibeam sonar, a remotely operated vehicle (ROV) and a towed camera system. Our results provide the first characterization of the Aleutian margin mid and lower slope benthic communities (micro-biota, foraminifera, macrofauna and megafauna), recognizing diverse habitats in a variety of settings. Our investigations also revealed that the geologic feature known as the "Ugamak Slide" is not a slide at all, and could not have resulted from a large 1946 earthquake. However, sediment disturbance appears to be a pervasive feature of this margin. We speculate that the deep-sea occurrence of high densities of Elphidium, typically a shallow-water foraminiferan, results from the influence of sediment redeposition from shallower habitats. Strong representation of cumacean, amphipod and tanaid crustaceans among the Unimak macrofauna may also reflect sediment instability. Although some faunal abundances decline with depth, habitat heterogeneity and disturbance generated by canyons and methane seepage appear to influence abundances of biota in ways that supercede any clear depth gradient in organic matter input. Measures of sediment organic matter and pigment content as well as C and N isotopic signatures were highly heterogeneous, although the availability of organic matter and the abundance of microorganisms in the upper sediment (1-5 cm) were positively correlated. We report the first methane seep on the Aleutian slope in the Unimak region (3263-3285 m), comprised of clam bed, pogonophoran field and carbonate habitats. Seep foraminiferal assemblages were dominated by agglutinated taxa, except for habitats above the seafloor on pogonophoran tubes. Numerous infaunal taxa in clam bed and pogonophoran field sediments and deep-sea "reef' cnidarians (e.g., corals and hydroids) residing on rocks near seepage sites exhibited light organic delta(13)C signatures indicative of chemosynthetic nutritional sources. The extensive geological, biogeochemical and biological heterogeneity as well as disturbance features observed on the Aleutian slope provide an attractive explanation for the exceptionally high biodiversity characteristic of the world's continental margins. (C) 2008 Elsevier Ltd. All rights reserved.

Species inhabiting deep-sea hydrothermal vents are strongly influenced by the geological setting, as it provides the chemical-rich fluids supporting the food web, creates the patchwork of seafloor habitat, and generates catastrophic disturbances that can eradicate entire communities. The patches of vent habitat host a network of communities (a metacommunity) connected by dispersal of planktonic larvae. The dynamics of the metacommunity are influenced not only by birth rates, death rates and interactions of populations at the local site, but also by regional influences on dispersal from different sites. The connections to other communities provide a mechanism for dynamics at a local site to affect features of the regional biota. In this paper, we explore the challenges and potential benefits of applying metacommunity theory to vent communities, with a particular focus on effects of disturbance. We synthesize field observations to inform models and identify data gaps that need to be addressed to answer key questions including: (1) what is the influence of the magnitude and rate of disturbance on ecological attributes, such as time to extinction or resilience in ametacommunity; (2) what interactions between local and regional processes control species diversity, and (3) which communities are "hot spots" of key ecological significance. We conclude by assessing our ability to evaluate resilience of vent metacommunities to human disturbance (e.g., deep-sea mining). Although the resilience of a few highly disturbed vent systems in the eastern Pacific has been quantified, these values cannot be generalized to remote locales in the western Pacific ormid Atlantic where disturbance rates are different and information on local controls is missing.